The use of color-forming coupler compounds which react with the development product of primary aromatic amino developing agents to form colored images upon photographic development is well known and has been the subject of many patents and other publications. The dyes formed in this way are usually insoluble in water and in the ordinary development and fixing solutions. Such coupler compounds may conventionally be added to the development solutions, or they may be incorporated into the photographic layers during the manufacture of the light sensitive elements. In this latter instance, the coupler compounds are referred to as "incorporated couplers". Incorporated couplers usually remain essentially immobile in their respective layer of the photographic element due largely to the fact that their molecules are fairly large. Immobile incorporated color-forming coupler compounds usually contain at least one so-called "ballasting" group in their molecule. Such "ballasted" photographic couplers are well known in the art and need not be dealt with in detail at this point. It should be understood that the incorporated couplers referred to herein are of the ballasted type.
Color-forming coupler compounds are generally used for subtractive color photography. Upon color development they form yellow, magenta or cyan dyes. For several important and well-known reasons, subtractive color photographic elements contain at least three distinct layers coated on a photographic support such as a transparent polymeric sheet. Generally, cyan-forming materials are placed in the color layer nearest the support, the silver halide in that layer being spectrally sensitized to the red region of the visible spectrum. In a color layer over the red-sensitized layer just described (possibly separated from that layer by one or more additional special purpose layers) is usually placed a magenta-forming layer, into which is incorporated magenta-forming color couplers. The silver halide in this magenta-forming layer is spectrally sensitized to the green region of the visible spectrum. In a third color-forming layer, which is coated over the green-sensitized layer (usually with a blue-light-absorbing layer between them) are incorporated yellow-forming coupler compounds. This yellow layer contains silver halide that is sensitive essentially to only the blue region of the visible spectrum.
Over the years, color photographic technology has been advanced and refined to the point that significant improvements are difficult to obtain. Meanwhile, consumers of film and paper based photographic products continue to demand products having better properties. Typical of the properties of concern to consumers are those directed to the sharpness and granularity of the final photographic product; i.e., the color photograph.
It is generally known that in order to improve the granularity of the image without decreasing the speed of the element a larger number of silver halide grains should be used. Granularity can also be improved by reducing the size of the silver halide grains, but this results in undesired loss of the photographic speed or sensitivity of the element. Thus, by increasing the number of silver halide grains (to improve granularity), one must increase the relative amount of silver halide in each layer. Since increases in the silver halide content of a layer generally caused concomitant increases in dye density (in each of the color layers) photographic products could result from using this approach (more silver halide) which have color densities that are too high. This, of course, would also be undesirable.
One method of overcoming the problems caused by too much color density is to use a so-called "competing coupler" during the development of the element. The competing coupler preferably forms either a colorless compound upon its reaction with oxidized color developer, or a dye which is soluble in the developer solution and can be removed by rinsing the developed element. The type and amount of competing coupler would be chosen so that the undesirable increase in color density referred to above would not occur.
A complication in our problem must be considered at this point. That is, while improving the granularity in the magenta and cyan layers by increasing the amount of silver halide in these layers, and by using higher levels of competing couplers (to compensate for excessive dye formation due to the additional developed silver halide), one must also increase the amount of silver halide in the top (yellow) color-forming layer. That is, however, undesirable, because the silver halide grains in the yellow color-forming layer scatter the green and red light that passes through the "yellow" dye layer to such an extent that the desired degree of sharpness in the magenta and cyan layers could not be obtained. However, by using only relatively low levels of silver halide in the yellow dye layer, the use of relatively higher concentrations of competing couplers (as described above) would be expected to cause an unacceptable loss of yellow color from the yellow dye layer.
It is an object of the present invention to overcome the apparent dilemma described above, so that one can obtain subtractive color photographic products which (i) exhibit the improved granularity characteristics described above (ii) have magenta and cyan dye levels which are not too high, and (iii) have yellow dye levels which are not too low. Thus, the resulting photographic color products also exhibit excellent color fidelity.